What does it take 6WD/8WD to be successful?

[IKE]

Somewhat contrary to my post, flex isn't always a bad thing though. It can make it tougher to turn, but it also can make it tougher to BE turned. You do want rigid rails along your chain paths though to make sure chains do not jump.

The nature of the kit 6x6 will give you a chassis with pretty good rail stiffness, and a pretty soft torsion to it. This will want to cause opposite corners to dig in when you are turning (bad), but also causes the same corners to dig in when someone is trying to push you around (this can be good if you are trying to hold your ground). You could probably do a pretty good master's thesis on torsionally rigidity and its effects of dynamic behaviour. I know I have read a dozen or so SAE papers on the subject.
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Again though the most important aspect is to understand your functional objectives and priorities. Initially we ranked our mobility objectives as:
Miving is given.
Ability to go over bumps
Ability to hold ground while shooting
Ability to maneuver well
Ability to move long distances quickly

This year we knew we wanted to clear the back row, and move to the midfield, thus the high priority on going over the bump. (In theory you can have 5 balls in a line that the opponent cannot stop you from scoring. That plus hanging equals 7 points which could win most matches.) In 2006, we were pushed around while trying to shoot, thus the hgih priority on holding ground. After the first competition, we found that more defense was played on the goals and balls than robot to robot and thus re-prioritized maneuverability over holding ground. Thus we changed from grippy wheels to the eventual migration to Omnis in the rear (we also needed less rock for ball collector improvements).
Understanding your objectives/priorities/assumptions helps you make decisions when you need to make improvements.

Amount of Rock, which wheels, and how you construct your frame are secondary to how you want it to ideally behave, and where you will make compromises. We consider these design attributes and/or tuning elements used to get the behaviour you want.

(P.S. I really liked the architecture of 201. If we didn't have all the experience and capability with 6x6, I would have pushed hard for an identical architecture. With a little more power, it would have been even more lethal.)